In a plain paper copying machine, toner images applied to the surface of paper or other recording medium are fixed by application of heat and pressure. In certain plain paper copying machines, fixation is accomplished by passing the image-bearing recording medium between a hot thermal fuser roll and a pressure roll. When this type of thermal fixation device is used the toner material is directly contacted by a roll surface, and a portion of the toner usually becomes adhered to the roll surface. 0n subsequent rotation of the roll, the adhered toner material may be re-deposited on the recording medium resulting in undesirable offset images, stains, or smears; or in severe cases the recording medium may stick to the adhered toner material on the roll and become wrapped around the roll.
To counter these problems, materials having good release properties such as silicone rubber or polytetrafluoroethylene are often used for the roll surfaces. Although improving the performance of the thermal fixation devices, use of silicone rubber or polytetrafluoroethylene roll surfaces alone does not eliminate the problem. Another approach is to include release agents with the toner materials, which prevent the toner materials from adhering to the roll surface. These oil-less toners improve the performance of the thermal fixation devices but again, particularly in the case of high-speed type copying machines, do not completely eliminate the problems associated with toner pick-up and transfer.
Toner pick-up by the rolls can be controlled by coating the surface of at least one of the rolls with a liquid release agent, such as a silicone oil. It is important that the release liquid be applied uniformly and in precise quantities to the surface of the roll. Too little liquid, or non-uniform surface coverage, will not prevent the toner from being picked up and re-deposited on the roll. On the other hand, excessive quantities of the release liquid may cause silicone rubber roll surfaces to swell and wrinkle, thus producing copies of unacceptable quality.
Devices to meter and coat a release liquid uniformly onto copy machine roll surfaces are described in Japanese laid-open patent number 62-178992. These devices consist of an oil permeation control layer adhered to a thick porous material which serves as a wick or reservoir for supplying oil to the permeation control layer. The permeation control layer controls the amount of oil delivered to the roll surface. The thick porous material to which the permeation control layer is adhered is typically a porous felt of Nomex (trademark) fibres, glass fibres, carbon fibres, polytetrafluoroethylene (PTFE) fibres, or other high temperature fibre. Fibres sold under the Nomex trademark are aramid fibres, a type of polyamide.
U.S. Pat. No. 4,668,537 describes a sliding-type applicator for release oil formed of a felt for holding the release oil, and a porous polytetrafluoroethylene (PTFE) membrane laminated over the felt by means of an FEP (tetrafluoroethylene-hexafluoropropylene copolymer) film. The FEP film is only applied along marginal portions of the felt.
U.S. Pat. Nos. 3,831,553 and 3,980,424 also describe arrangements for oiling or cleaning a fuser roll.
European patent application 91309005.6 (0479564) laid open on Apr. 8, 1992 discloses an oil-filled reservoir in the form of a roller. The device comprises a liquid permeation control layer of porous expanded PTFE membrane adhered to a porous tubular reservoir. The reservoir comprises an open-cell thermosetting polymer foam which requires to be internally reinforced to obtain the strength, resilience, and heat resistance needed for high durability in use as part of a hot toner image fixation mechanism in a plain paper copying machine. The thermosetting polymer foam is a melamine resin, a polyimide resin, a phenolic resin, or bismaleimidetriazine resin. An internal reinforcing layer is formed of silicone oil and silicone rubber within the outer surface of the reservoir roller.